Resistance element and electric iron containing the same



June 27, 1950 c H, SPARK 2,512,692 RESISTANCE ELEMENT ANDELECTRIC IRON CONTAINING THE SAME Filed Jan. 15, 1947 2 Sheets-Sheet 1 June 27, 1950 c, s Lm 2,512,692

" RESISTANCE ELEMENT AND ELECTRIC IRON CONTAINING THE SAME Filed Jan. 15, 1947 2 Sheets-Sheet '2 Patented June 27, 1950' STATES NT OFFICE RESISTANCE ELEMENT AND ELECTRICI'RON CONTAINING THE SAME Charles H. Sparklin, Chicago; Ill.,--assignor.to Birtman Electric Company, a :corporation .of

Illinois 8 Application January 15, 1947 ,tSe1-ial N 0. 722,127

.I 2 Claims.

"Thi invention relates to aresistance element and more particularly; to the method of introducing the element into. an. electric iron and the iron so produced.

This application is a continuation-in-part of my copending application Serial No. 524,850 filed March 3, 1944, now abandoned.

/ Various methods of combining a resistance element with an electric iron have been'employed in the past. In somejcasesthe resistance material was-embedded in mud on-the top of the sole plate .of the iron. "This method isobjectionable because it does not. provideadequate insulation and will not withstand physical shock. In some cases .the resistance element was produced in the form of a rod which is'anchoredon'top ofthe sole rplate.

Various other methods have also been employed.

None of these devices has had the-proper dew. gree of permanence. ease of; replacement, :and

calorific 'efii ciency. which are combined in the present invention.

The invention isil'lustrated inthe drawings in whichFig. 1 is a' plan view of the sole plate of a preferred formof the iron; Fi 2 is av section takenalongthedine 2--2 of Fig. 1; Fig. 3 is a I sectional View like Fig. 2 illustrating the first yphase of-forming the. embeddedresistance-elementyFig. 4 is a-i similar view illustrating the second step; Fig. 5. is a sectional elevational of a suitable plungeremployed in carrying out step 2;

Fig. 6 is a view similar to Fig. 4, illustrating the iron after the completion of the third and fourth steps; Fig. '7 is a view of one form ofthe resistance element; Fig. 8 is a viewsimilar to Fig. 6 and showing theiron afterpcompletion of the fifth forming step; Fig. 9 is a sectional-elevation illustrating a plungerandstamping employed in wthelfifth forming step; Figs 1-0 is a View illustrating-a preferred form of resistance element mounting; Fig. 11 is a detail view of the end of the ceramic device 'shown'in'Fig. illustrating the method of introducing .the. resistance wire into the ceramic core; Fig. 12 is a plan view of the .iron withthe resistance elementinsta'lled and attached; and Fig. 13 is a sectional'view.=taken along the line I3l.3-in Fig. .10.

As shown in Figs. 1 and 2, the preferred sole upp r edge oil-the semi-cylinder being approxinmately levelwith the normal top of .the sole plate.

In forming the resistance element, each of the "slots isvfilled to 'an appropriate point with dry,

very-finely powdered, magnesium oxide, zirconiumsilicate, orother suitable powdered insulating material which has the-property of cohering when pressed. The volume of material employed will depend upon the compressibility of the powder'and the thickness-oi refractory and insulating coatingd'esired. Ordinarily :the amount used should bev such as toiorm a thin- -semi-tubular coating having'a'thickness of from to. inch. Ordinarily about /2 inch depth of magnesium oxide powder willaproduce a coating of suitable thickness upon-compression. A layer of this powder 30 isrindicated in Fig. 3. The :powder is then .compressed, for example, by a plunger 3l having a semi-cylindrical head 32 under a pressure of from 2.5 to (items per square inch, for example,

3 tons perrsquare inchr The HQCk233 of the plung- 1 er extendsthenomplete length ofone of'the slots 21 -or :22 and fits tightly enough therein so that the:p.owder will'not-be forced out around it. The

:head"32 isnarrowervthan the neck-and forms two longitudinal shoulders and 35 which cor- ;respond to thethickness ofthe coating-36 which isiproduced upon compressioni'of the powder. Theoperation of the plunger 3| upon the powder in'.the';S10ts' produces a. coherent self-sustaining 'semi tubular bed. of refractory insulating mate- -;.rial.. aszshown iniFig. 4. The resistanceelement 40, in the form'of a helix having closely spaced convolutions and 1' preferably ;formed about a ceramic ,core 41,. is; then land within the bed formed by. the coating136. The resistance ele- :ment maybe of the usuahNichrome wire. wThe wmethod'of embeddingwhichis here employed permits the use of larger wire than is :usually employed. A suitable. wire has a; diameter of I 0.028inch and it may becoiled around a ceramic core having a diameter aboutlA-inch in convolutions separated by as'little-as. .020 inch. vThe ends of the wire, as they extend beyond the ceramic'core, are preferably doubled back. as. in-

..edicated at. 42::1Thisforms a loop: 13 ateach end of the wire which may be usedforattachment to-the' posts- 44 -and 45, and also has been found 1 the ends have been" doubled back as indicated.

When the resistance element has been inserted desirablein protecting the'wire The life of the resistance element is considerably. greater when upon the bed 36, additional-powder 50 is. added substantially to fill' theslots 2| and 22 asshown in Fig. 6. T This powder is suitablythesameas l -=the powderemploye'dfor the-underlying bedgwThe powder is then compressed under a considerably greater pressure such as 25 to 40 tons per square inch, for example 38 tons per square inch, as shown in Figs. 8 and 9. This last compressing is preferably by the use of a plunger 5! having a neck 52 which presses upon a pressure stamping 53. This stamping is in the form of a boat having the same length as the slots 2| and 22. This boat has a bottom 54, and integral upstanding side walls 55 and 56 which are preferably upturned at an angle slightly less than 90. The metal of the boat is selected to have considerable resilience so that the side walls 55 and 56 tend to engage the flanges 23 and 24 which form the walls of the slot, and to retain the boat therein. The boat thus acts as a closure member tightly sealing the insulating refractory material within the sole plate. It also acts as a heat distributing member which carries heat radiated or conducted into it from the resistance element into the metal of the sole plate and thus considerably reduces radiation losses to the air.

The bottom layer bed 36 having been compressed under the relatively light pressure of 2.5 to 6 tons per square inch is still deformable under additional pressure. When the resistance element wire 40 and core 4! unit is laid on the bed, covered with powdered insulating material 50, and the powder 50 compressed at a pressure pressure makes a unitary rigid insulating structure consisting of the core 4! and the surrounding insulating material with the resistance element 40 rigidly held in the surrounding material. The insulating structure is quite solid and completely fills the spaces between the inner surfaces of the slots 2! and 22 and the stampings 53 so that no air pockets are left to later expand under heat. The resistance element wire is solidly held on all sides so that when heated and cooled it can not move under the forces of expansion and contraction. The insulating material and resistance element wire is, in effect, formed into a unitary solid structure wth the sole plate and the resistance element lasts as long as the sole plate itself.

During the formation of the embedded resistance element, the ends of the slots may be closed in any desirable fashion, either by temporary closure members applied individually or collectively to the slots, or by mechanism which may be a permanent part of the pressing apparatus. This closing off of the ends ofthe slots is facilitated by having the ends parallel and by having the slots of equal length. Thus a single closing off element may be employed at each end if desired.

An electric iron containing the new sole plate has been operated for 20,000 hours without failure, at which point the test was stopped. The ordinary electric iron heating unit operates from 50' to 750 hours before failure, while the best previous irons with a heating element insulated tion of relatively small pressure of 2.5 to 6 tons per square inch used in forming'the bottom bed36 4 and the extremely large pressure of 25 to 40 tons per square inch used on the complete structure. The final pressure causes the resistance wire to be embedded in and surrounded by the insulating material and the material to become quite hard and solid. The resistance wire can not move under expansion and contraction caused by the heating and cooling of the wire. Thus the wire cant snap in two and the coils cant contact their neighbors to cause shorting. In the finished sole plate structure the insulating material is almost as hard as the sole plate and the resistance wire. In Figs. 10 and 11 I have shown a special form of ceramic core for the resistance element. This comprises a ceramic or other insulating material of considerable strength in the form of an elongated generally cylindrical member 50, at each end of whichis a cutaway portion Bl extending from the end of the last helical convolution 52 to'the end of the core. The material is' put away on substantially a diameter 63 as shown in Fig. 13, and a feeding hole 54 is formed transversely of the neck 55 remaining. In winding the resistance wire upon the core, the twisted double end 700i the resistance wire is passed inwardly through the opening 5 1, as shown in Fig. 11, and is then bent at right angles thereto. This effectively anchors the wire and permits the wire to be wound tightly upon the grooves 82. On the completion of the winding, the residual end of the wire, likewise doubled back upon itself and twisted, is drawn inwardly through the hole 54 and bent axially of the rod.

The foregoing detailed description has been given for clearness of understanding only, and

no unnecessary limitations should be understood therefrom.

I claim: 7 1. In forming an electric heating element, the method which comprises compressing powdered insulating material under a pressure of 2.5 to 6 tons per square inch within an elongated depression in a metal heating plate to form a coherent insulating bed, imposing a resistance element thereon, supplying additional powdered insulating material to cover the resistance element, and compressing the added insulating material under a pressure of 25 to 40 tons per square inch.

2. In forming an electric heating element, the method which comprises compressing powdered insulating material under a relatively heavy pressure within an elongated depression in a metal heating plate to form a coherent insulating bed, imposing a resistance element thereon, supplying additional powdered insulating material to cover the resistance element, and compressing the added insulating material under a relatively heavy pressure that is substantially 4 to 16 times greater than said first pressure.

CHARLES H. SPARKLIN.

nnrnnnnons strap The following references are of record in the file of this patent:

UNITED s'rAIns PATENTS Numb er Name Date 1,432,435 Abbot Oct. 17, 1922 1,551,868 Clark et a1 Sept. 1, 1925 1,745,526 Braun et a1 Feb. 4, 1930 1,767,084 Lightfoot June 24, 1930 1,783,554 Backer Dec. 2, 1930 2,053,405 Myers Sept. 8, 1936 2,222,192 1 Arnold et al Nov. 19, 1940 

